The invention relates to a semiconductor device comprising a semiconductor body provided with a circuit element in the form of an electrical resistor comprising a resistor zone with a comparatively high resistivity between two connection regions with a comparatively low resistivity, the interspacing between the connection regions being so small that velocity saturation of charge carriers takes place in the resistor zone during operation. Such a device is known, for example, from the book "Physics of Semiconductor Devices" by S. M. Sze, 2nd ed., John Wiley & Sons, pp. 352-354. ("Sze")
The demand for compact resistor elements of high resistance value increases continuously in the manufacture of integrated circuits as a result of the continuous reduction of the dimensions of the other components, such as transistors. The transistors, for example, and thus the current through the amplifier become increasingly smaller in a differential amplifier with shared emitters, so that it is necessary to increase the load resistances correspondingly in order to obtain the same amplification. In usual resistor elements, however, an increase in the resistance value means an increase in the space occupied by the resistor elements, which is in conflict with the efforts to obtain ever smaller dimensions. In addition, this increase in the space occupation is accompanied by an increase in the parasitic capacitance, which adversely affects the frequency behaviour of the circuit.
It is furthermore important that the temperature sensitivity of the resistor should be as small as possible. The temperature sensitivity is fairly great in usual resistors in integrated circuits, where the resistor comprises a doped zone or a layer of doped polycrystalline silicon (poly), in the sense that the resistance rises fairly strongly upon a rise in temperature, which causes various properties of the circuit to change. In addition, thermal effects may give rise to temperature gradients across the integrated circuit so that, for example, the ratios between the various resistance values are disturbed such as, for example, in the case of the differential amplifier mentioned above which is so designed that the load resistances are basically identical.
It is also important for many applications that the value of the resistor which is obtained at the end of the manufacturing process should correspond as accurately as possible to a value previously defined in the design of the circuit. When conventional resistor elements are used, the resistance value depends not only on the dimensions, parameters which in general can be well controlled by means of the present-day advanced manufacturing techniques, but also on a quantity such as the net doping concentration, which has a much wider spread. Sze describes a resistor element with reference to FIG. 32 on p. 353 wherein saturation of the drift velocity of charge carriers in a high electric field in the resistor zone is utilized. The device comprises a p-type semiconductor body which is provided at the surface with a comparatively weakly doped n-type resistor zone which is provided on either side with highly-doped n-type connection zones. When the voltage across the resistor is sufficiently high, velocity saturation takes place in the semiconductor material of the resistor. Upon a further increase of the voltage, the current will rise only very little, so that a high (differential) resistance can be obtained. The resistance value obtained in the saturation range is practically independent here of the doping concentration and less dependent on the temperature than in conventional resistors. The resistor in this embodiment behaves as a conventional diffused resistor at lower voltages, with a comparatively low resistance value which is determined by the doping concentration, so that the resistor exhibits the disadvantages described above in this range. A high resistance is often required also at lower voltages, for example in view of a low dissipation.